Organohalosilanes, halosilanes, and in particular methylchlorosilanes, are the building blocks from which silicone polymers are produced. Organohalosilanes and halosilanes are commercially produced by what is commonly called “the direct process”, in which silicon metal is reacted with an organic halide or hydrogen chloride, optionally in the presence of a catalyst. Various aspects of the direct process are well known in the art, and have been described in patent literature.
In, for example, the commercial production of methylchlorosilanes by the direct process, finely ground silicon metal powder is reacted with methyl chloride in the presence of a catalyst by fluidizing the silicon powder in a fluid bed by passing methyl chloride gas through at a temperature of between 200° C. and 500° C. At the end of the reaction, there remains in the fluid bed, solids material. Similar steps are taken and similar direct process solids material is produced when manufacturing halosilanes.
In the commercial production of methylchlorosilanes, after the removal of the methylchlorosilanes from the fluid bed reactor, the direct process solids material remaining in the fluid bed reactor comprises mainly silicon metal and silicon oxides with minor amounts of other materials such as catalyst, unreacted organic halide, carbon residues, impurities and reaction product.
It is well known that direct process solids material can be hazardous if left in an unpassivated state. When in contact with moisture, such as atmospheric moisture, it evolves hydrogen gas, and it is highly susceptible to atmospheric oxidation and self-heating, which represents a potential fire hazard. Consequently, methods have been developed to passivate direct process solids. One such method is through quenching by reaction with an alkaline substance such as an aqueous lime solution. However, this method requires long reaction times, energy to heat the reaction, and subsequent separation steps to remove metals such as silicon, copper, zinc and aluminum. These negatives, along with the added large amount of water that remains after the reaction, make this process expensive. Another method of passivating direct process solids is to mix the direct process solids material with clay; however, this method increases the amount of waste generated, and the direct process solids material is still active for a period after mixing with the clay. Examples of quenching and/or passivating methods are described in U.S. Pat. No. 5,000,934 (Dow Corning); Russian Patent No. 2118561 (State Scientific Centre of the Russian Federation); and US Patent Application Publication U.S. 2004/0029713.
The present inventors have found that direct process solids may be passivated using a mixture of clay, water, and base. The method has economic advantages such as reducing waste, equipment maintenance, labor, raw material costs, and the amount of passivating and inert compounds present from the clay. Reducing the inert materials also results in an increased amount of valuable copper in the final material, because the copper from the direct process solids is less diluted by the inert material. In addition to the economic benefits, the new method also improves other properties of the resulting material. The new method reduces the passivated product's dustiness by improving its ability to be rewet. It reduces the environmental, health and safety concerns of neutralizing the activity of the direct process solids, and it requires less quenching time and improves the consistency of the clay-direct process solids compositions.